One common type of non-destructive inspection (NDI) or non-destructive test (NDT) is an eddy current inspection. During this inspection process, eddy current sensors impart and detect eddy currents within a structure, particularly in metallic and other conductive structures. The data acquired by an eddy current sensor may be processed and displayed so as to identify cracks within and/or corrosion upon the structure. While eddy current inspection is advantageous for detecting cracks, eddy current inspection may be utilized in other applications known to those skilled in the art such as dent profile mapping, lightning strike evaluation, fire damage evaluation and the like.
Both automated and manual eddy current inspection systems have been developed. In automated inspection systems, one or more eddy current sensors are moved in a controlled fashion along the structure that is being inspected. The data collected by the eddy current sensor(s) is processed and associated with the location on the structure from where the data was obtained. While automated eddy current inspection systems provide for relatively fast and accurate inspections, the automated systems are quite expensive. In many cases, structures must be inspected in the field since, for example, it may not be feasible or it may be too expensive and/or time-consuming to transport the structure to an offsite laboratory for inspection. In these instances, the automated eddy current inspection systems may prove to be too bulky for routine field inspections. Additionally, the use of an automated eddy current inspection system in the field may further be hampered by the inability of an automated system to be powered by a local power supply, such as batteries, and the automated eddy current inspection system may, instead, need to be connected to a remote power supply via bulky power cables.
As such, eddy current sensors that may be manually scanned by a technician, such as during the routine field inspection of the structure, are available. Typically, a trained technician holds the sensor and moves the sensor along the structure such that the eddy current sensor inspects all desired portions of the structure. A typical eddy current probe includes a single sensing element, although some eddy current probes include a linear array of coils. Current may be induced in the coil(s) based upon an input drive signal, typically consisting of an alternating current (AC) input provided by the eddy current sensor, and the current induced in that portion of the structure proximate the coil(s) as a result of the AC input signal. Based upon the current induced within each coil, at least one characteristic, such as the electrical conductivity, of those portions of the structure proximate the respective coils may be determined.
Conventional eddy current sensors adapted for manual inspection of a structure also generally include a position encoder. The position encoder is initialized with the eddy current sensor disposed at a predetermined reference position relative to the structure. The output of the position encoder can therefore be analyzed to determine the current position of the eddy current sensor relative to the structure. Thus, the measurements of the current induced within each coil may be associated with a corresponding location upon the surface of the structure. Thus, a spatial map of at least one characteristic of the structure may be constructed from which cracks, corrosion or the like may be identified.
Utilizing conventional eddy current sensors during the manual inspection of a structure, a two-dimensional image of the structure and, in particular, of at least one characteristic of the structure could only be constructed once the sensor had been moved along the surface of the structure with the current induced in each coil of the measured at each position of the eddy current sensor. Thus, a two-dimensional image of the structure cannot be created in real time. Moreover, for the measurement of the current induced in each coil of the eddy current sensor to be meaningful and for the resulting two-dimensional image to be accurate, the position of the eddy current sensor must be accurately provided by the position encoder. Thus, any slippage between the position encoder and the underlying structure would render any subsequently obtained measurements of the current induced in the coil(s) inaccurate since the relative position upon the surface of the structure at which those measurements were obtained cannot be accurately defined. Moreover, since the generation of the two-dimensional image relies upon the movement of the sensor in one direction, the movement of the eddy current sensor in any other direction would also prevent a two-dimensional image of the structure from being properly created. As such, the quality of the inspection is dependent, in large part, upon the performance of the technician in moving the eddy current sensor along the surface of the structure. Thus, the manual scanning of structures with a conventional eddy current sensor is time-consuming, labor-intensive and prone to human error. Additionally, manual scanning of an eddy current sensor over the surface of a structure may fatigue the technician.
As such, it would be desirable to develop an improved eddy current probe and associated inspection method that permits a structure to be scanned more quickly, while permitting the eddy current probe to be moved in any desired direction along the surface of the structure. In addition, it would be desirable to provide an improved eddy current probe and associated inspection method that is capable of producing a real time display of at least one characteristic of the structure under inspection.